This invention relates to a device comprising an electronic circuit for processing an analog electric signal and a voltage multiplying (or boosting) circuit intended to be connected to an electrical energy supply source, to provide a supply voltage to said electronic circuit.
Many forms of apparatus that comprise a device of the above kind, e.g. hearing aids, remote controls for toys, miniature radioreceivers, etc., are of such small size that the electric energy supply source of the device may only consist of a cell or a miniature rechargeable battery. Such a cell or battery necessarily only has a single electro-chemical element.
A cell or a battery having only a single element supplies when new a voltage of 1.5 to 1.7 V or a voltage of 2 to 2.2 V, respectively. These voltages obviously decrease when the cell or the battery discharges.
The electronic circuit comprised by a device of the above mentioned kind generally includes one or more amplifiers that require a minimum supply voltage of about 2 V to ensure proper operation.
That is why such a device generally includes a voltage multiplying circuit to produce the supply voltage needed by the amplifiers from the voltage supplied by the above mentioned cell or battery.
The small size of the various forms of apparatus using these devices and the need to produce them at the lowest possible cost moreover make it imperative for all of the components of the electronic device to be formed in one and the same integrated circuit.
Now, a voltage multiplying circuit that is produced in an integrated circuit, having no component external to the integrated circuit, has rather poor electrical characteristics.
In particular, its internal resistance is high so that its output voltage very much depends on the current that is used by the circuits it supplies.
It is in practice not possible to correct these defects, even partially, by inserting a voltage stabiliser between the voltage multiplier and the circuits it supplies because such a stabiliser, to operate properly, would require an input voltage that is a good deal higher than the voltage it is required to supply.
Now, a voltage multiplying circuit like the one mentioned above cannot in practice supply the voltage stabiliser with this high input voltage because of the voltage drops that necessarily occur in the various stages of the voltage multiplying circuit and which are not much less than the voltage supplied by the cell or the battery.